**6. Conclusions and outlook**

CFD is a widely used tool that has played a role in biotechnology for many years and is constantly gaining in popularity. It can be used to determine classical parameters such as power input, mixing time and oxygen transfer, as well as to carry out further evaluations with spatial and time resolutions. CFD is also an excellent approach for determining hydrodynamic stress. However, depending on the

bioreactor system and parameters, different modelling approaches should be selected to determine these parameters. Investigations have shown that for bioreactor modelling, the Fluent commercial software from Ansys dominates, followed by OpenFOAM, an open source solution. Very few authors compute on GPUs, however they still use CPUs. Even tough when used in conjunction with the latest software solutions, GPUs cost less, use less power and perform faster computations. In spite of the considerable computing power currently available, phenomena such as turbulence and gas bubble breakup in industry-relevant simulations, such as bioreactors, are still approximated using semi-empirical models. In the future, more powerful GPUs or even quantum processors for QCFD will increase computational power, and methods like PINN will speed up computations, potentially making it possible to eliminate the need for these models and perform even more accurate and faster simulations. In the second part of the series, the methods described here for process engineering characterisation are demonstrated based on real-world examples, using both commercial and open-source software.
